I've been testing this, and I think I got out all the bugs =) Link: http://cf.gy/minecraftpe.html
Video if you haven't seen:
This might only work on chrome atm (I'm pretty sure firefox nightly supports file apis as well).
Edit: you are missing Camera (456).
Post if you have any problems!
Looks pretty cool! I'll have to look at the source.
I tried it in Chrome Mobile for Android - opening a Survival level.dat works, but Android refuses to download the modified file.